1. Field of the Invention
This invention relates to novel catalysts for olefin polymerization. More particularly, it is concerned with a process for the production of polyolefins which comprises polymerizing or copolymerizing olefins with a catalyst obtained by activating with organometallic compounds solid powders obtained by co-pulverizing (1) a metal halide selected from the group consisting of magnesium halides and manganese halides, (2) a compound represented by the general formula B(OR).sub.n X.sub.3-n where n is a number of the range 0&lt;n.ltoreq.3, X represents a halogen atom and R is a hydrocarbon radical containing from 1 to 20 carbon atoms and may be alike or different and (3) a titanium compound and/or vanadium compound, thereby remarkably increasing the yield of the polymer per the solid as well as that per the transition metal with a result that the step for removing the catalyst becomes unnecessary due to decrease in the catalyst residue in the polymer, and moreover remarkably increasing impact strength of the resulting polymer.
Moreover, a polyolefin prepared by polymerizing an olefin using the catalyst of this invention has not only a very high bulk specific gravity but also a large average particle size and therefore this invention provides the following important advantages:
(1) scattering of polymer particles into vapour phase space in the reactor due to stirring and the like is so decreased that adhering of polymer particles to the reactor wall and the like is very decreased and therefore a stable operation can be done,
(2) adhering of polymer particles to the inner walls of pipes is so small that the slurry transportation can be more easily done,
(3) in the solvent removal step, due to large sizes of polymer particles, scattering of polymer particles with steam is not caused and therefore the solvent removal step can be easily effected, and
(4) also in the drying step and the pelleting step, scattering of polymer particles is not caused and these steps can be easily effected like the solvent removal step.
As described above, the use of the catalyst of this invention facilitates handling of the polymer slurry and enables higher productivity per unit reaction volume.
2. Description of the Prior Art
In the art prior to the invention, an improvement in catalytic activity for the polymerization of olefins has been made by the use of catalysts prepared by a combination of a transition metal compound in advance carried on a magnesium compound such as MgO or MgCl.sub.2 or a manganese compound such as MnCl.sub.2 or MnI.sub.2 with an organoaluminum compound. Simultaneous improvement in impact strength of the resulting polyolefin, however, has not satisfactorily achieved by any of the known catalysts. Need has recently been arisen in the resin for injection molding for higher impact, particularly Izot impact strength; especially so in the transportation art as represented by the crate for beer. Therefore, there has been a high demand for development of catalysts with a high activity as well as affording a higher impact strength in the resulting polyolefins.
We have previously proposed the use of catalysts comprising a combination of solid powders from co-pulverization of a titanium compound such as titanium tetrachloride or a titanium alkoxide and a carrier prepared by co-pulverizing a magnesium halide and a compound of the general formula Al(OR).sub.3 wherein R is alkyl containing 1-4 carbon atoms and three R may be alike or different or one prepared by co-pulverizing a magnesium halide and a compound of the general formula Si(OR).sub.m X.sub.4-m wherein R is a hydrocarbon radical containing 1-20 carbon atoms, X represents a halogen atom and m is in the range 0&lt;m.ltoreq.4 with an organometallic compound, with which polyolefins with a high impact strength can be produced.